Blowing up a city and giving them instant death with no suffering like that is not the same thing. At least in Ock's mind.

Exactly. Plus, I doubt Ock even considered the individuals who'd die in his schemes -- those victims would just be all a faceless mass. The only people I remember him murdering specifically are adults (and, yes, he's pretty heartless about that).

Strange as it may seem, scheming to turn Manhattan into a radioactive wasteland (as he intended in the Owl/Black Cat arc way back when) is a far cry from physically striking some poor dumb little kid who's wearing a vulture costume. (Not to mention using children as henchmen... ick! At least Ock's hires were always professionals.)